Apparatus and method for communication

ABSTRACT

An eigen value expansion section  103  calculates eigen values and eigen vectors in a correlation matrix or covariance matrix of input signals. When the ratio between a maximum eigen value and other eigen values is equal to or lower than a threshold, an assignment method selection section  104  selects a code assignment method whereby systematic bits are transmitted with their respective eigen vectors. As a result, a communication apparatus  100  transmits a systematic bit X with the respective eigen vectors. On the other hand, when the ratio between a maximum eigen value and other eigen values is greater than the threshold, the assignment method selection section  104  selects a code assignment method whereby systematic bits are transmitted with only the eigen vector having the maximum eigen value. As a result, the communication apparatus  100  transmits the systematic bit X with only the eigen vector having the maximum eigen value. This makes it possible to obtain an effect of improving sufficient communication quality even when the difference between the maximum eigen value and other eigen values is large in a communication system which combines a turbo code and MIMO.

TECHNICAL FIELD

The present invention relates to a communication apparatus andcommunication method used in a communication system which combines aturbo code and MIMO (Multiple-Input Multiple-Output).

BACKGROUND ART

For a radio communication, an error correcting code is a technologyindispensable for transmitting/receiving high-reliability information. Aturbo code is becoming a focus of attention as a correcting code havinga strong error correcting capacity in recent years.

A basic turbo coder is constructed of a parallel connection of aplurality of recursive systematic convolutional coders (RSC) through aninterleaver as shown in FIG. 1 and outputs a systematic bit (informationbit) X and parity bits Y1, Y2.

Furthermore, MIMO (Multiple-Input Multiple-Output) is becoming a focusof attention in recent years as a system for effectively realizinghigh-speed transmission using a limited frequency band.

The MIMO is a system which uses an array antenna for both transmissionand reception to simultaneously transmit/receive independent signals onthe same band using a plurality of eigen vectors. Using this MIMO makesit possible to expand a transmission capacity without expanding thefrequency band.

There is also an on-going study for improving communication quality bycombining a turbo code and MIMO.

Here, when the ratio between systematic bits and parity bits transmittedis equal among eigen vectors, the amount of improvement in communicationquality increases as the respective eigen values become more uniform andthe effect of improvement in communication quality decreases as thedifference between a maximum eigen value and other eigen valuesincreases.

However, in a conventional communication system, magnitudes of eigenvalues are not taken into consideration and the ratio between systematicbits and parity bits of each eigen vector always remains constant, andtherefore when a difference between a maximum eigen value and othereigen values is large, the effect of improvement in communicationquality using a turbo code decreases.

Especially in a situation such as a base station of a cellular system inwhich an antenna on the transmitting side is set high for the purpose ofcovering a wide range, a maximum eigen value becomes a value by farlarger than other eigen values, and therefore it seems necessary to addcertain improvement.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a communicationapparatus and communication method in a communication system thatcombines a turbo code and MIMO capable of obtaining sufficient effectsof improvement in communication quality even when there is a largedifference between a maximum eigen value and other eigen values.

This object can be attained by measuring a ratio between the maximumeigen value and other eigen values and controlling the type of codeddata to be transmitted with the respective eigen vectors based on themeasurement result.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of the configuration of a turbo coder;

FIG. 2 illustrates an example of a communication system using MIMO;

FIG. 3 is a block diagram showing the configuration of a communicationapparatus according to Embodiment 1 of the present invention;

FIG. 4A illustrates coded data transmitted with each eigen vector of thecommunication apparatus according to Embodiment 1 of the presentinvention;

FIG. 4B illustrates coded data transmitted with each eigen vector of thecommunication apparatus according to Embodiment 1 of the presentinvention;

FIG. 5 is a block diagram showing the configuration of a communicationapparatus according to Embodiment 2 of the present invention;

FIG. 6A illustrates coded data transmitted with each eigen vector of thecommunication apparatus according to Embodiment 2 of the presentinvention; and

FIG. 6B illustrates coded data transmitted with each eigen vector of thecommunication apparatus according to Embodiment 2 of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present inventor has come up with the present invention noting thatsince an amount of improvement in communication quality of MIMO isproportional to the magnitude of an eigen value, when a maximum eigenvalue is much greater than other eigen values, transmitting systematicbits with only an eigen vector having the maximum eigen value makes itpossible to obtain a coding gain and improve the amount of improvementin communication quality.

With reference now to the attached drawings, embodiments of the presentinvention will be explained in detail below. As shown in thecommunication system in FIG. 2, a case where data istransmitted/received between a communication apparatus 10 and acommunication apparatus 20 each provided with an array antenna using twoeigen vectors A, B (suppose the eigen vector of a maximum eigen value is“A”) will be explained. Also suppose that the communication apparatus ofeach embodiment encodes transmission data using the turbo coder shown inFIG. 1.

EMBODIMENT 1

FIG. 3 is a block diagram showing the configuration of a communicationapparatus according to Embodiment 1 of the present invention. Thecommunication apparatus 100 in FIG. 3 is one of the communicationapparatuses 10, 20 shown in FIG. 2.

The communication apparatus 100 in FIG. 3 is mainly constructed ofantenna elements 101-1 to m, reception RF sections 102-1 to m, an eigenvalue expansion section 103, an assignment method selection section 104,a beam forming section 105, demodulation sections 106, 107, anassignment method decision section 108, a turbo decoding section 109, aturbo coding section 151, a code assignment section 152, a repetitionsection 153, modulation sections 154, 155 and transmission RF sections156-1 to m.

The plurality of antenna elements 101-1 to m constitute an adaptivearray antenna, receive a signal sent from the other party ofcommunication, output the signal to the corresponding reception RFsections 102-1 to m and transmit signals output from the correspondingtransmission RF sections 156-1 to m to the other party of communicationby radio.

The reception RF sections 102-1 to m carry out radio processing such asamplification and down-conversion on the signals received by thecorresponding antenna elements 101-1 to m and output baseband signals tothe eigen value expansion section 103 and beam forming section 105.

The eigen value expansion section 103 calculates eigen values and eigenvectors of a correlation matrix or covariance matrix of input signalsbased on the signals output from the reception RF sections 102-1 to mand outputs the eigen values to the assignment method selection section104 and the eigen vectors to the beam forming section 105.

The assignment method selection section 104 calculates the ratio betweenthe maximum eigen value and other eigen values, compares this ratio witha preset threshold, selects a code assignment method based on thedecision result and outputs a command indicating the selected codeassignment method (hereinafter referred to as “assignment methodindication command”) to the code assignment section 152 and modulationsection 154. The processing of the assignment method selection section104 will be explained more specifically later.

The beam forming section 105 combines the signals output from thereception RF sections 102-1 to m using the eigen vectors output from theeigen value expansion section 103 and outputs the combined signal to thedemodulation sections 106, 107. Furthermore, the beam forming section105 divides signals output from the modulation sections 154, 155 into mportions corresponding in number to the antenna elements, carries outcomplex multiplication processing on each signal using eigen vectors andoutputs these signals to the transmission RF sections 156-1 to m.

The demodulation section 106 demodulates the signal which is output fromthe beam forming section 105 and received with the eigen vector A,outputs a control signal to the assignment method decision section 108and outputs the coded data to the turbo decoding section 109.Furthermore, the demodulation section 107 demodulates the signal whichis output from the beam forming section 105 and received with the eigenvector B and outputs the coded data to the turbo decoding section 109.

The assignment method decision section 108 decides the code assignmentmethod of the other party of communication based on the assignmentmethod indication command included in the output signal of thedemodulation section 106 and outputs the decision result to the turbodecoding section 109.

The turbo decoding section 109 carries out turbo decoding processing onthe coded data output from the demodulation sections 106, 107 based onthe decision result of the assignment method decision section 108 andextracts the received data.

The turbo coding section 151 carries out turbo coding processing on thetransmission data and outputs coded data made up of a systematic bit Xand parity bits Y1, Y2 to the code assignment section 152.

The code assignment section 152 outputs the coded data output from theturbo coding section 151 to the modulation section 154 or modulationsection 155 based on the assignment method indication command from theassignment method selection section 104 and outputs a control signal tothe repetition section 153. Details of the processing by the codeassignment section 152 will be described in detail later.

The repetition section 153 carries out repetition processing on codeddata (parity bit Y2) output from the turbo coding section 151 andoutputs the coded data after repetition processing to the modulationsection 155 according to the control signal from the code assignmentsection 152.

The modulation section 154 modulates data to be transmitted with theeigen vector A, which is the coded data output from the code assignmentsection 152 and an assignment method indication command from theassignment method selection section 104 and outputs the modulated signalto the beam forming section 105.

The modulation section 155 modulates data to be transmitted with theeigen vector B, which is the coded data output from the code assignmentsection 152 or the repetition section 153 and outputs the modulatedsignal to the beam forming section 105.

The transmission RF sections 156-1 to m carry out radio processing suchas amplification and up-conversion on the signal output from the beamforming section 105 and output the processed signals to thecorresponding antenna elements 101-1 to m.

Next, details of the processing by the assignment method selectionsection 104 and code assignment section 152 will be explained using FIG.4A and FIG. 4B. FIG. 4A and FIG. 4B illustrate data transmitted with therespective eigen vectors of this embodiment. FIG. 4A shows coded datatransmitted with the eigen vectors when the ratio between a maximumeigen value and other eigen values is equal to or lower than athreshold, while FIG. 4B shows coded data transmitted with the eigenvectors when the ratio between a maximum eigen value and other eigenvalues is greater than the threshold.

When the ratio between a maximum eigen value and other eigen values isequal to or lower than the threshold, the assignment method selectionsection 104 selects a code assignment method of transmitting systematicbits with the respective eigen vectors and outputs a command “0” whichindicates this selection result.

When code assignment section 152 receives the assignment methodindication command “0” from the assignment method selection section 104,it outputs a systematic bit X and a parity bit Y1 to the modulationsection 154 and outputs the systematic bit X and parity bit Y2 to themodulation section 155, and controls the repetition section 153 so as tostop outputting coded data.

As a result, the communication apparatus 100 transmits the systematicbit X with the respective eigen vectors A, B as shown in FIG. 4A.

On the other hand, when the ratio between the maximum eigen value andother eigen values is greater than the threshold, the assignment methodselection section 104 selects a code assignment method of transmittingsystematic bits with only an eigen vector having a maximum eigen valueand outputs a command “1” indicating this selection result.

When the code assignment section 152 receives the assignment methodindication command “1” from the assignment method selection section 104,it outputs the systematic bit X and parity bit Y1 to the modulationsection 154 and controls the repetition section 153 so as to outputcoded data to the modulation section 155.

As a result, the communication apparatus 100 transmits the systematicbit X with only the eigen vector A having a maximum eigen value andtransmits the parity bit Y2 repeated with the eigen vector B as shown inFIG. 4B. Using repetition with eigen vectors having small eigen valuescan improve signal quality and make the quality of different beamsuniform.

Thus, by transmitting systematic bits with the respective eigen vectorswhen the respective eigen values are uniform and transmitting systematicbits with only the eigen vector having the maximum eigen value when themaximum eigen value is much greater than the other eigen values, it ispossible to obtain a maximum effect by combining a turbo code and MIMOthrough improvement of communication quality.

In both cases of FIG. 4A and FIG. 4B, the communication apparatus 100transmits an assignment method indication command with the eigen vectorA having the maximum eigen value. This can reduce decision errors whenthe receiving side decides the assignment method and improve stabilityof the system.

In the cases of FIG. 4A and FIG. 4B, a signal transmitted from the otherparty of communication with the eigen vector A having the maximum eigenvalue is demodulated by the demodulation section 106, and therefore theassignment method decision section 108 extracts an assignment methodindication command from the output signal of the demodulation section106, decides the content (“0” or “1”) and can thereby know the codeassignment method of the other party of communication.

EMBODIMENT 2

FIG. 5 is a block diagram showing the configuration of a communicationapparatus according to Embodiment 2 of the present invention and thecommunication apparatus 200 in FIG. 5 is one of the communicationapparatuses 10, 20 shown in FIG. 2.

In the communication apparatus 200 shown in FIG. 5, components common tothose of the communication apparatus 100 shown in FIG. 3 are assignedthe same reference numerals as those in FIG. 3 and explanations thereofwill be omitted. The communication apparatus 200 in FIG. 5 adopts theconfiguration of the communication apparatus 100 in FIG. 3 with apuncturing section 201 added. Furthermore, in the communicationapparatus in FIG. 5, a code assignment section 202 carries outprocessing different from the code assignment section 152 in FIG. 3.

A turbo coding section 151 outputs a systematic bit X to the codeassignment section 202 and outputs parity bits Y1, Y2 to the puncturingsection 201.

The puncturing section 201 punctures the parity bits Y1, Y2 and outputsthe remaining parity bits Y1, Y2 to the code assignment section 202 andoutputs the punctured parity bits Y1′, Y2′ to a repetition section 153.

The repetition section 153 carries out repetition processing on thecoded data (parity bits Y1′, Y2′) output from the puncturing section 201and outputs the coded data after the repetition processing according toa control signal from the code assignment section 202 to a modulationsection 155.

Based on an assignment method indication command from an assignmentmethod selection section 104, the code assignment section 202 outputsthe coded data output from the turbo coding section 151 and puncturingsection 201 to the modulation section 154 or modulation section 155 andoutputs a control signal to the repetition section 153.

More specifically, when the code assignment section 202 receives anassignment method indication command “0” from the assignment methodselection section 104, it outputs the systematic bit X and parity bitsY1, Y2 to the modulation sections 154, 155 respectively and controls therepetition section 153 so as to stop outputting coded data.

As a result, as shown in FIG. 6A, the communication apparatus 100transmits the systematic bit X and parity bits Y1, Y2 with eigen vectorsA, B. Therefore, it is possible to complete signals transmitted from therespective eigen vectors as one coding unit.

On the other hand, when the code assignment section 202 receives anassignment method indication command “1” from the assignment methodselection section 104, it outputs the systematic bit X and parity bitsY1, Y2 to the modulation section 154 and controls the repetition section153 so as to output the coded data to the modulation section 155.

As a result, as shown in FIG. 6B, the communication apparatus 100transmits the systematic bit X, parity bits Y1, Y2 with the eigen vectorA and transmits the parity bits Y1′, Y2′ punctured with the eigen vectorB and repeated. Therefore, it is possible to complete a signaltransmitted from the eigen vector A having the maximum eigen value asone coding unit and assign an auxiliary role when decoding to the codeddata transmitted from the eigen vector B having a value other than themaximum eigen value.

As in the case of Embodiment 1, in any one of FIG. 6A, FIG. 6B, thecommunication apparatus 200 transmits the assignment method indicationcommand from the eigen vector A having the maximum eigen value.

Furthermore, the above described embodiments have explained the casewith two eigen vectors, but the present invention places no limit on thenumber of eigen vectors. Furthermore, the configuration of the turbocoder in the present invention is not limited to the one illustrated inFIG. 1.

As described above, according to the present invention, thecommunication system which combines a turbo code and MIMO controls thetype of coded data to be transmitted with the respective eigen vectorsbased on the ratio between the maximum eigen value and other eigenvalues, and can thereby obtain a maximum effect of combining the turbocode and MIMO in realizing improvement of communication quality.

This application is based on the Japanese Patent Application No.2003-040217 filed on Feb. 18, 2003, entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a communication apparatusin a communication system which combines a turbo code and MIMO.

1. A communication apparatus used in a system which transmits/receivesindependent signals using an array antenna for both transmission andreception with a plurality of eigen vectors, comprising: a turbo codingsection that carries out turbo coding on transmission data and obtainscoded data of a systematic bit and a parity bit; an eigen valuecalculation section that calculates an eigen value of said each eigenvector; an assignment method selection section that selects anassignment method of coded data to be transmitted with said each eigenvector based on the ratio between a maximum eigen value and other eigenvalues; and a transmission section that transmits predetermined codeddata with said each eigen vector based on the selected assignmentmethod.
 2. The communication apparatus according to claim 1, whereinwhen the ratio between the maximum eigen value and other eigen values isgreater than a predetermined threshold, said assignment method selectionsection selects a first assignment method whereby the systematic bit istransmitted only from an eigen vector having a maximum eigen value andselects a second assignment method whereby the systematic bit istransmitted from all eigen vectors when the ratio between the maximumeigen value and other eigen values is equal to or lower than saidthreshold.
 3. The communication apparatus according to claim 2, furthercomprising a repetition section that repeats parity bits, wherein whensaid assignment method selection section selects said first assignmentmethod, said transmission section transmits parity bits after saidrepetition from an eigen vector having other than the maximum eigenvalue.
 4. The communication apparatus according to claim 3, furthercomprising a puncturing section that punctures parity bits, wherein saidrepetition section repeats punctured parity bits, and when saidassignment method selection section selects said first assignmentmethod, said transmission section transmits systematic bits andremaining parity bits through said puncturing from an eigen vectorhaving a maximum eigen value and transmits parity bits after saidrepetition from eigen vectors other than the maximum eigen value.
 5. Thecommunication apparatus according to claim 1, wherein said transmissionsection transmits an assignment method indication command indicating theassignment method selected by said assignment method selection sectionfrom an eigen vector having a maximum eigen value.
 6. A communicationapparatus used in a system which transmits/receives independent signalsusing an array antenna for both transmission and reception with aplurality of eigen vectors, which carries out radio communication withthe communication apparatus according to claim 5, comprising: anassignment method decision section that extracts an assignment methodindication command from a signal transmitted with an eigen vector havinga maximum eigen value and decides the assignment method of coded datacorresponding to the respective eigen vectors; and a turbo decodingsection that carries out turbo decoding on the coded data transmittedwith the respective eigen vectors based on the decision result of saidassignment method decision section.
 7. A communication method used in asystem which transmits/receives independent signals using an arrayantenna for both transmission and reception with a plurality of eigenvectors, comprising: a step of carrying out turbo coding on transmissiondata and obtaining coded data of systematic bits and parity bits; a stepof calculating eigen values of said respective eigen vectors; a step ofselecting an assignment method of coded data transmitted from saidrespective eigen vectors based on the ratio between a maximum eigenvalue and other eigen values; and a step of transmitting predeterminedcoded data with said respective eigen vectors based on the selectedassignment method.